In current Laser Activated Remote Phosphor (LARP) applications, glass is deposited on a ceramic converter or a dichroic coated substrate by liquid glass dosing. Alternatively, a microgram sized fragment may be cut from a thin glass fiber and heated until the fiber melts. In both processes, the glass must remain melted from the time of deposition through final assembly, due to the large difference in the coefficient of thermal expansion (CTE) between the glass versus the dichroic coated substrate and the ceramic converter. With the large difference in CTE between the glass and the material it is bonded to, the glass may spall off upon cooling. This requires the glass dosing process, which is inherently difficult to maintain and control, to be an integral part of the assembly. Any difficulty with dosing requires a shut-down of production.
For the liquid dosing process, control over bubbles in the glass fiber dosing process, weight control, contamination and special registering (correct location for glass) are inherently difficult. It should be noted that the Te—Ze—Al—Na-Oxide glass is very susceptible to reduction, resulting in dark glass and bubbles when contaminated with organic matter. Experience with liquid dosing and cut fiber dosing has shown large variations in glass thickness at the bonding interface.
Alternatively, a drop-cast method, or dispensing method, has been used where liquid glass droplets may be used to form a bonding film between a wavelength converter and dichroic layer for LARP applications. Optical fibers may be cut into tiny microgram pieces and melted onto the carrier substrate before or during the bonding process of the converter platelets. Such process, however, along with being slow, could give non-uniform thickness within the bonding area if not optimized.